Synergistic Catalyst Combination for the Preparation of Radiation Curable Oligomers

ABSTRACT

Radiation curable coating compositions are disclosed. In some embodiments, the coating compositions are used to coat substrates such as packaging materials and the like for the storage of food and beverages. The coating compositions may have a (meth)acrylate functional polyether polyol prepared by reacting an epoxidized vegetable oil in the presence of a phosphoric acid compound to form an epoxy phosphate, and reacting the epoxy phosphate with a hydroxyl functional (meth)acrylatein the presence of an acid catalyst to form the(meth)acrylate functional polyether polyol.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to radiation curable coating compositions,methods of coating substrates with the coating compositions, andsubstrates coated with the coating compositions.

2. Description of Related Art

Many currently available radiation curable coatings, such as those curedwith ultra-violet (“UV”) radiation or electron beam (“EB”) radiation,have a tendency to be inflexible after curing and prone to high levelsof shrinkage. Consequently, many radiation curable coatings arerecognized to be inadequate in terms of direct to metal adhesion,formability and retort resistance, which are some of the desiredproperties for rigid packaging coating applications. Adhesion andextensibility inadequacies have been found when the coatings were usedfor flexible packaging.

Commonly-owned International Patent publication WO 2008/151286 describesradiation curable oligomers prepared from an epoxidized vegetable oiland a hydroxyl functional material in the presence of a strong acidcatalyst.

The radiation curable coating compositions of the invention aim to solvesome of the aforementioned inadequacies. The coating compositions can beused, inter alia, as packaging coatings for food and beverage packagingand containers. They can be formulated to provide improved adhesion,flexibility, and formability compared to some commercial radiationcurable coating compositions.

SUMMARY OF THE INVENTION

Aliphatic epoxide groups in the epoxidized vegetable oils of WO2008/151286 are generally less reactive than glycidyl epoxy groups. WO2008/151286 explains that strong acid catalysts such as zinc triflatesare suitable to catalyze the reaction of epoxidized vegetable oils withhydroxyl functional compounds. However, even with these strong acidcatalysts, hydroxyl functional (meth)acrylates like butane diolmonoacrylate and hydroxy ethyl acrylate might thermally polymerize athigh temperature, even in the presence of polymerization inhibitors. Asa result, it is difficult to prepare radiation curable coatingcompositions with high conversion from epoxidized vegetable oils andhydroxyl functional (meth)acrylates.

The present invention includes radiation curable coating compositionshaving a (meth)acrylate functional polyether polyol, processes forproducing the coating compositions, methods of coating substrates withthe coating compositions, and substrates coated with the coatingcompositions. Such processes can be performed in a single reactor or inmultiple reactors.

In some embodiments of the invention, a coating composition having a(meth)acrylate functional polyether polyol is prepared by a methodcomprising reacting an epoxidized vegetable oil with a phosphoric acidcompound to form an epoxy phosphate, and then reacting the epoxyphosphate with a hydroxyl functional (meth)acrylate in the presence ofan acid catalyst to form the (meth)acrylate functional polyether polyol.In some embodiments, the acid catalyst comprises a triflic acid, atriflate salt of a metal of Group IIA, IIB, IIIA, IIIB or VIIIA of thePeriodic Table of Elements (according to the IUPAC 1970 convention), amixture of the triflates salts, or a mixture thereof.

It has been found that a phosphoric acid compound and an acid catalystfunction as a synergistic catalyst combination during the preparation ofradiation curable coating compositions. The phosphoric acid compoundincreases the reaction rate of the hydroxyl functional (meth)acrylatewith the epoxidized vegetable oil. The phosphate functionality of theepoxy phosphate helps adhere the radiation cured coating composition tothe substrate. In addition, the epoxy phosphate significantly enhancesthe effectiveness of the acid catalyst used to form the (meth)acrylatefunctional polyether polyol, allowing the acid catalyst to be used at alower concentration while achieving a higher reaction rate and morecomplete conversion. As a result, compared to WO 2008/151286, the amountof the acid catalyst can be reduced by a factor of at least about 10,while conversion of the epoxide groups in the epoxidized vegetable oilcan be increased from about 90% to about 99.9% at the same reactiontemperature and the same reaction time.

The present invention includes methods of coating a substrate byapplying the coating composition to the substrate. Substrates coatedwith the coating compositions are also disclosed. In some embodiments,the substrate is a can or packaging.

DETAILED DESCRIPTION OF THE INVENTION

As used in the afore-discussed embodiments and other embodiments of thedisclosure and claims described herein, the following terms generallyhave the meaning as indicated, but these meanings are not meant to limitthe scope of the invention if the benefit of the invention is achievedby inferring a broader meaning to the following terms.

The present invention includes substrates coated at least in part with acoating composition of the invention and methods for coating thesubstrates. The term “substrate” as used herein includes, withoutlimitation, cans, metal cans, easy-open-ends, packaging, containers,receptacles, or any portions thereof used to hold, touch or contact anytype of food or beverage. Also, the terms “substrate”, “food can(s)”,“food containers” and the like include, for non-limiting example, “canends”, which can be stamped from can end stock and used in the packagingof food and beverages.

The present invention includes coating compositions having a(meth)acrylate functional polyether polyol and methods for preparing thecoating compositions. The coating compositions may be prepared byreacting an epoxidized vegetable oil with a phosphoric acid compound toform an epoxy phosphate, and reacting the epoxy phosphate with ahydroxyl functional (meth)acrylate in the presence of an acid catalystto form the (meth)acrylate functional polyether polyol.

In some embodiments, the phosphoric acid compound includes phosphoricacid, super phosphoric acid, an aqueous solution of the foregoing, or amixture thereof. In some embodiments, the phosphoric acid compound ispresent in an amount from about 0.001 to about 25 wt % of the(meth)acrylate functional polyether polyol.

During the reaction of the epoxidized vegetable oil with the phosphoricacid compound, some of the epoxide groups do not react with thephosphoric acid compound. As a result, these epoxide groups areavailable to react with the hydroxyl functional (meth)acrylate toproduce the (meth)acrylate functional polyether polyol.

The epoxidized vegetable oil can be used alone or in combination withother epoxidized vegetable oils. Epoxidized vegetable oils can beprepared from vegetable oils by, for non-limiting example, addinghydrogen peroxide and formic or acetic acid to the vegetable oil, andthen holding the mixture at an elevated temperature until some or all ofthe carbon-carbon double bonds are converted to epoxide groups.

Vegetable oils contain primarily glycerides which are triesters ofglycerol and fatty acids with varying degrees of unsaturation. Fornon-limiting example, epoxidized vegetable oils for use in the inventioncan be made from vegetable oils (fatty acid triglycerides) such aswithout limitation, esters of glycerol and fatty acids having an alkylchain of about 12 to about 24 carbon atoms. Fatty acid glycerides whichare triglycerides in unsaturated glyceride oils are generally referredto as drying oils or semidrying oils. Drying oils include, fornon-limiting example, linseed oil, perilla oil and combinations thereof,while semidrying oils include, without limitation, tall oil, soy beanoil, safflower oil and combinations thereof. Triglyceride oils in someembodiments have identical fatty acid chains or alternatively havedifferent fatty acid chains attached to the same glycerol molecule. Insome embodiments, the oils have fatty acid chains containingnon-conjugated double bonds. In some embodiments, single double bond orconjugated double bond fatty acid chains are used in minor amounts.Double bond unsaturation in glycerides can be measured by iodine value(number) which indicates the degree of double bond unsaturation in thefatty acid chains. Unsaturated fatty acid glyceride oils employed insome embodiments of the invention have an iodine value greater thanabout 25 and alternatively between about 100 and about 210.

Naturally occurring vegetable oils for use in the invention can be fornon-limiting example, mixtures of fatty acid chains present asglycerides, and include without limitation a distribution of fatty acidesters of glyceride, where the fatty acid distribution may be random butwithin an established range that may vary moderately depending on thegrowing conditions of the vegetable source. Soybean oil is employed insome embodiments which comprises approximately about 11% palmitic, about4% stearic, about 25% oleic, about 51% linolenic, and about 9% linoleicfatty acids, where oleic, linoleic and linolenic are unsaturated fattyacids. Unsaturated vegetable oils employed in some embodiments of theinvention, include without limitation, glyceride oils containingnon-conjugated unsaturated fatty acid glyceride esters such as, withoutlimitation, linoleic and linolenic fatty acids.

Unsaturated glyceride oils include, without limitation, corn oil,cottonseed oil, rapeseed oil, hempseed oil, linseed oil, wild mustardoil, peanut oil, perilla oil, poppyseed oil, rapeseed oil, saffloweroil, sesame oil, soy bean oil, sunflower oil, canola oil, tall oil, andmixtures thereof. Fatty acid glycerides for use in the inventioninclude, for non-limiting example, those which contain linoleic andlinolenic fatty acid chains, oils such as without limitation, hempseedoil, linseed oil, perilla oil, poppyseed oil, safflower oil, soy beanoil, sunflower oil, canola oil, tall oil, grapeseed oil, rattonseed oil,corn oil, and similar oils which contain high levels of linoleic andlinolenic fatty acid glyceride. Glycerides can contain lesser amounts ofsaturated fatty acids in some embodiments. For non-limiting example, soybean oil can be employed which contains predominantly linoleic andlinolenic fatty acid glycerides. Combinations of such oils are employedin some embodiments of the invention. Vegetable oils can by fully orpartially epoxidized by known processes, such as for non-limitingexample, using acids such as, without limitation, peroxy acid forepoxidation of unsaturated double bonds of the unsaturated vegetableoil. Unsaturated glyceride oils employed in some embodiments includemono-, di-glycerides and mixtures thereof with tri-glycerides or fattyacid esters of saturated and unsaturated fatty acids.

In some embodiments, the epoxidized vegetable oil comprises corn oil,cottonseed oil, grapeseed oil, hempseed oil, linseed oil, wild mustardoil, peanut oil, perilla oil, poppyseed oil, rapeseed oil, saffloweroil, sesame oil, soy bean oil, sunflower oil, canola oil, tall oil, afatty acid ester, monoglyceride or diglyceride of such oils, or amixture thereof.

Commercially available sources of epoxidized vegetable oils are used insome embodiments of the invention such as, for non-limiting example,epoxidized soy oil sold under the trade designations “VIKOLOX” and“VIKOFLEX 7170” available from Arkema, Inc, “DRAPEX 6.8” available fromChemtura Corporation, and “PLAS-CHECK 775” available from Ferro Corp.Other epoxidized vegetable oils for use in the invention include, fornon-limiting example, epoxidized linseed oil sold under the tradedesignations “VIKOFLEX 7190” available from Arkema, Inc. and “DRAPEX10.4” available from Chemtura Corporation, epoxidized cotton seed oil,epoxidized carthamus oil and mixtures thereof. Epoxidized soy bean oilis employed in some embodiments.

The hydroxyl functional (meth)acrylate may include without limitation4-hydroxy butyl (meth)acrylate, hydroxyl ethyl (meth)acrylate, hydroxylpropyl (meth)acrylate and the like, as well as combinations thereof.Along with the hydroxyl functional (meth)acrylate, one or more hydroxylfunctional materials may be present as diluents. Such hydroxylfunctional materials may include without limitation alcohols, polyols,polyesters, polyethers, polycarbonates, and the like, as well asmixtures thereof. The hydroxyl functional (meth)acrylate and thehydroxyl functional material may each be present during the formation ofthe epoxy phosphate. The hydroxyl functional (meth)acrylate and thehydroxyl functional material may also each be present during theformation of the (meth)acrylate functional polyether polyol.

In some embodiments, the hydroxyl functional (meth)acrylate is presentin an amount from about 1:99 to about 95:5 in a weight ratio of thehydroxyl functional (meth)acrylate to the epoxidized vegetable oil, andalternatively from about 5:95 to about 40:60. In some embodiments, theequivalent ratio of hydroxyl functionality of the hydroxyl functional(meth)acrylate to oxirane functionality in the epoxidized vegetable oilis from about 0.1:1 to about 3:1. In some embodiments, the equivalentratio of hydroxyl functionality to oxirane functionality in theepoxidized vegetable oil is from about 0.2:1 to about 3:1. In someembodiments, the equivalent ratio of hydroxyl functionality to oxiranefunctionality in the epoxidized vegetable oil is about 0.2:1. Theepoxidized vegetable oil may be present in an amount from about 1 toabout 95 parts based on the total weight of the (meth)acrylatefunctional polyether polyol. The hydroxyl functional (meth)acrylate maybe present in an amount of from about 1 to about 95 parts of the(meth)acrylate functional polyether polyol.

In certain embodiments, the (meth)acrylate functional polyether polyolmay be present in an amount from about 1 to about 100 wt % of thecoating composition.

The epoxy phosphate and the hydroxyl functional (meth)acrylate may bereacted in the presence of an acid catalyst. In some embodiments, theacid catalyst comprises a triflic acid, a triflate salt of a metal ofGroup IIA, IIB, IIIA, IIIB or VIIIA of the Periodic Table of Elements(according to the IUPAC 1970 convention), a mixture of the triflatessalts, or a mixture thereof. The reaction may be at a temperature ofabout 50 to about 160° C. or from about 80 to about 120° C. In someembodiments, the acid catalyst has a dissociation constant in an aqueoussolution (pKa) less than about 4. In some embodiments, the acid catalysthas a hydrophobe attached to the acid. In some embodiments, the amountof the acid catalyst can range from about 1 ppm to about 10,000 ppm, andalternatively from about 10 ppm to about 1,000 ppm, based on the totalweight of the reaction mixture.

Acid catalysts additionally include, for non-limiting example, the GroupIIA metal triflate catalysts such as without limitation magnesiumtriflate, the Group IIB metal triflate catalysts such as withoutlimitation zinc and cadmium triflate, the Group IIIA metal triflatecatalysts such as without limitation lanthanum triflate, the Group IIIBmetal triflate catalysts such as without limitation aluminum triflate,and the Group VIIIA metal triflate catalysts such as without limitationcobalt triflate, and combinations thereof. Some embodiments of theinvention employ an acid catalyst, such as a metal triflate catalyst, inthe form of a solution in an organic solvent. Examples of solventsinclude, without limitation, water, alcohols such as n-butanol, ethanol,propanol, and the like, as well as aromatic hydrocarbon solvents,cycloaliphatic polar solvents such as, for non-limiting example,cycloaliphatic ketones (e.g. cyclohexanone), polar aliphatic solvents,such as, for non-limiting example, alkoxyalkanols, 2-methoxyethanol, nonhydroxyl functional solvents, and mixtures thereof.

The reaction of the phosphoric acid compound with the epoxidizedvegetable oil is rapid, even at low temperatures, so mixing thephosphoric acid compound into the hydroxyl functional (meth)acrylatehelps to moderate this reaction and produce a more uniform epoxyphosphate. The epoxy phosphate may be formed by the addition of thephosphoric acid compound to the epoxidized vegetable oil at about 20 toabout 100° C.

Radiation curable coating compositions of the invention can includeconventional additives known to those skilled in the art, such aswithout limitation, flow agents, surface active agents, defoamers,anti-cratering additives, lubricants, and cure catalysts. In addition,(meth)acrylate monomers can be blended to control viscosity and di- andpoly(meth)acrylate monomers and (meth)acrylate functional oligomers canbe blended to achieve desired film properties.

In some embodiments of the invention, one or more coating compositionsare applied to a substrate, such as for non-limiting example, cans,metal cans, easy-open-ends, packaging, containers, receptacles, canends, or any portions thereof used to hold or touch any type of food orbeverage. In some embodiments, one or more coatings are applied inaddition to the coating compositions of the present invention, such asfor non-limiting example, a prime coat may be applied between thesubstrate and the coating composition.

The coating compositions can be applied to substrates in any mannerknown to those skilled in the art. In some embodiments, the coatingcompositions are sprayed or roll coated onto a substrate. After thecoating composition is applied, the coating composition may be curedwith electron beam or ultraviolet radiation.

The resulting coating compositions are applied in some embodiments byconventional methods known in the coating industry. For substratesintended as beverage containers, the coating are applied in someembodiments at a rate in the range from about 0.5 milligrams to about 15milligrams per square inch of polymer coating per square inch of exposedsubstrate surface. Radiation curable coating compositions are generallyroll applied to flat substrates and then cured under UV lamps orelectron beams. With electron beams, dosages of about 0.5 to 10 mrad aresuitable for good cure under a nitrogen atmosphere.

EXAMPLES

The invention will be further described by reference to the followingnon-limiting examples. It should be understood that variations andmodifications of these examples can be made by those skilled in the artwithout departing from the spirit and scope of the invention.

Example 1 Preparation of (Meth)Acrylate Functional Polyether Polyol

36 grams of butane diol monoacrylate and 0.5 grams of super phosphoricacid were added to 110 grams of epoxidized soy bean oil and 0.05 gramsof phenothiazine with stirring at room temperature to form a mixture.The mixture was warmed to 90° C. in a water bath under an air purge. Themixture was stirred for 1 hour. Next, 36 grams of butane diolmonoacrylate and 0.10 milliliters of Nacure Super A-218 (25% zinctriflate) were added to the mixture and held for 1 hour. A moderateexotherm was noted (to 98° C. in 20 minutes). Oxirane titration at theend of the reaction indicated that 99.9% conversion of the epoxidegroups.

What is claimed is:
 1. A radiation curable coating compositioncomprising a (meth)acrylate functional polyether polyol prepared by amethod comprising: a) reacting an epoxidized vegetable oil with aphosphoric acid compound to form an epoxy phosphate; b) reacting theepoxy phosphate with a hydroxyl functional (meth)acrylate in thepresence of an acid catalyst to form the (meth)acrylate functionalpolyether polyol.
 2. The coating composition of claim 1, wherein thereaction of step a) is conducted in the presence of a hydroxylfunctional material.
 3. The coating composition of claim 1, wherein thehydroxyl functional (meth)acrylate is blended with a hydroxyl functionalmaterial.
 4. The coating composition of claim 1, wherein the acidcatalyst comprises a triflic acid, a triflate salt of a metal of GroupIIA, IIB, IIIA, IIIB or VIIIA of the Periodic Table of Elements(according to the IUPAC 1970 convention), a mixture of the triflatessalts, or a mixture thereof.
 5. The coating composition of claim 1,wherein the hydroxyl functional (meth)acrylate comprises 4-hydroxy butyl(meth)acrylate, hydroxy ethyl (meth)acrylate, hydroxyl propyl(meth)acrylate, or a mixture thereof.
 6. The coating composition ofclaim 1, wherein the phosphoric acid compound comprises phosphoric acid,super phosphoric acid, an aqueous solution of the foregoing, or amixture thereof.
 7. The coating composition of claim 1, wherein thephosphoric acid compound is present in an amount from about 0.001 toabout 25 wt % of the (meth)acrylate functional polyether polyol.
 8. Amethod of coating a substrate comprising: a) applying the coatingcomposition of claim 1 to the substrate; and b) curing the coatingcomposition with electron beam or ultraviolet radiation.
 9. The methodof claim 8, wherein the reaction of step a) is conducted in the presenceof a hydroxyl functional material.
 10. The method of claim 8, whereinthe hydroxyl functional (meth)acrylate is blended with a hydroxylfunctional material.
 11. The method of claim 8, wherein the acidcatalyst comprises a triflic acid, a triflate salt of a metal of GroupIIA, IIB, IIIA, IIIB or VIIIA of the Periodic Table of Elements(according to the IUPAC 1970 convention), a mixture of the triflatessalts, or a mixture thereof.
 12. The method of claim 8, wherein thehydroxyl functional (meth)acrylate comprises 4-hydroxy butyl(meth)acrylate, hydroxy ethyl (meth)acrylate, hydroxyl propyl(meth)acrylate, or a mixture thereof.
 13. The method of claim 8, whereinthe phosphoric acid compound comprises phosphoric acid, super phosphoricacid, an aqueous solution of the foregoing, or a mixture thereof. 14.The method of claim 8, wherein the phosphoric acid compound is presentin an amount from about 0.01 to about 25 wt % of the (meth)acrylatefunctional polyether polyol.
 15. A substrate coated with the coatingcomposition of claim
 1. 16. A substrate coated with the coatingcomposition of claim 8.